Bays eyes were very blue from 3 months on and have stayed that way (hes 3.5yrs now). Astins sometimes look grey/brownish and sometimes blue so we cant tell what they are going to settle on!!
I had very dark brown eyes when i was little then when i was 9 they changed to hazel which they are now.
My niece had blue eyes until she was 2.5yrs then they changes to a funny hazel brown.
I dont think there is a set time that they change so i would say just put down what they are at present